when to switch a hobby/interest to a business

I've managed and started many businesses, and continue to work in a business advisory role today. I've recently initiated the closing of my fourth start-up (mostly due to lack of time, but there were other factors as well), and am looking to go 'off the grid' for a while.

I'm going to be taking up a personal interest project of working on an online game I've designed for fun. Having had a few failed gaming start-up attempts due to mismanagement of other people, I plan to do this all on my own (again, for fun and the learning experience).

My question is, at what point (if any) in the process of developing a working game, should I start looking at wrapping a business model around it? Theoretically, if I enjoy the project and I'm good at it, I could do most of it on my own. Of course, running a business is another beast altogether, and I doubt I could continue to maintain my interests and operate a privately run business at the same time (especially if one is based on the other).

Just remember once it becomes your business it may no longer be so enjoyable. So have a new hobby ready to give you another activity in your life.

When your hobby can pay your bills -- pull a switch and focus all you time on it.